Autoignition for igniting gas-generative compositions used in inflator devices for protective passive restraints

ABSTRACT

An autoignition composition for a gas generant for an airbag or the like. The autoignition comprises a mixture of CuO as the oxidizer in a weight percentage of 45% to 75%, and aminoguanidine nitrate as the fuel in a weight percentage of 25% to 55%. To increase the flame temperature of the mixture, a metal fuel such as magnesium or aluminum can be added.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gas generant compositions and, more particularly, to gas generant compositions employed in various autoignition devices, such as vehicle occupant passive restraint systems (airbags), fire suppressants, aircraft escape chutes, life rafts and the like.

2. Description of the Prior Art

Many devices, such as protective passive restraints or air bags used in motor vehicles. escape slide chutes. life rafts, and the like, are normally stored in a deflated state and are inflated with gas substantially instantaneously at the time of need. Such devices are generally stored and used in close proximity to humans and, therefore, must be designed with a high safety factor which is effective under all conceivable ambient conditions.

Inflation is sometimes accomplished solely by means of a gas generative composition. At other times, inflation is accomplished by means of a gas, such as air, nitrogen, carbon dioxide, helium, and the like, which is stored under pressure and further pressurized and supplemented at the time of use by the addition of high temperature combustion gas products produced by the burning of a gas-generative composition.

It is critical that the gas-generative composition be capable of safe and reliable storage without decomposition or ignition at temperatures which are likely to be encountered in a motor vehicle or other storage environment. For example. temperatures as high as about 107° C. (225° C.) may reasonably be experienced It is also important that substantially all the combustion products generated during use be non-toxic. non-corrosive, non-flammable, particularly where the inflator device is stored in a closed environment, such as a passenger compartment of a motor vehicle.

Igniters are well known in the art for igniting gas-generative compositions in inflators for protective passive restraints used in motor vehicles. In a typical inflator device, the igniter itself may be ignited either directly, or indirectly via an intermediate or auxiliary igniter, by an electrically activated initiator (e.g., squib) which is responsive to a sensed impact of the motor vehicle.

Due to the emphasis on weight reduction for improving fuel mileage in motor vehicles, inflator units are often formed form light weight materials, such as aluminum, that can lose strength and mechanical integrity at temperatures significantly above the normal operating temperature of the unit. Although the temperature required for the unit to lose strength and mechanical integrity is much higher than will be encountered in normal vehicle use, these temperatures are readily reached in, for example, a vehicle fire. As the operating pressure of the standard pyrotechnics increases with increasing temperature, a gas generator composition at its autoignition temperature will produce an operating pressure that is too high for a pressure vessel that was designed for minimum weight. Moreover, the melting point of many gas generator compositions is low enough for the gas generator composition to be molten at the autoignition temperature of the composition, which can result in a loss of ballistic control and excessive operating pressures. Therefore, in a vehicle fire, for example, the ignition of the gas generator composition can result in an explosion in which fragments of the inflation unit are propelled at dangerous and potentially lethal velocities.

To prevent such explosions, inflator units have typically been provided with an autoignition propellant (sometimes abbreviated hereinafter as “AIP”) that will autoignite and initiate the combustion of the main gas generating pyrotechnic charge at a temperature below that at which the shell or housing of the inflator unit begins to soften and lose structural integrity.

Some gas generator or pyrotechnic devices require a non-chlorate low temperature autoignition material to safely ignite the main pyrotechnic charge contained within the device when the device is exposed to a high temperature environment or a flame. This is especially true when the main pyrotechnic charge contains ammonium nitrate as an ingredient. For these types of pyrotechnic devices the required autoignition temperature of the autoignition material is often within the range of 140° C. to 160° C.

It would be desirable if an AIP composition could be provided which satisfies the need to reduce the ignition temperature of the propellant composition below its autoignition temperature while, at the same time, exhibits a high degree of stability and compatibility. The composition of the present invention meets such need.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an autoignition composition comprising a mixture of cupric oxide (AKA, CuO, copper valance 2 oxide) as the oxidizer and aminoguanidine nitrate as the fuel. The weight percentage of CuO lies within the range of 45% to 75%, and the weight percentage of aminoguanidine nitrate lies within the range of 25% to 55%.

If it is desired to increase the flame temperature of the mixture, a metal such as magnesium (Mg) or aluminum (Al) can be added to the mixture in a weight percentage of less than 20%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a DSC (Differential Scanning calorimetry) analysis of pure aminoguanidine nitrate; and

FIG. 2 is a DSC (Differential Scanning calorimetry) analysis of a mixture consisting of 55% CuO by weight and 45% aminoguanidine nitrate by weight.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a chlorate free low temperature autoignition composition based upon oxidizers and/or fuels that have melting point temperatures >135° C. and <160° C. In particular the present invention uses aminoguanidine nitrate as the fuel whose melting temperature is approximately with the range of 144° C. to 147° C. With the correct selection of an oxidizer when the aminoguanidine nitrate melts, ignition occurs. FIG. 1 shows a DSC (Differential Scanning calorimetry) analysis of pure aminoguanidine nitrate. The melt point (onset of endotherm) can be clearly seen at approximately 145° C.

The present invention in particular uses the oxidizer cupric oxide (AKA; CuO, copper valance 2 oxide) with aminoguanidine nitrate. FIG. 2 shows a DSC (Differential Scanning calorimetry) analysis of a mixture consisting of CuO (55% by weight) and aminoguanidine nitrate (45% by weight). The melt (endotherm) of the aminoguanidine nitrate can be seen which is immediately followed by a large exotherm. Hot plate test analysis of 0.5 gram sample of the mixture confirmed ignition with a large sustained flame at 150° C. Furthermore, automotive airbag inflators that use an ammonium nitrate based main generant material were put through a slow heating environment and all inflators benignly deployed when the skin temperature of the inflators reached 152° C.

Stoichiometric reacton equation is:

5 CuO+2 CH₇N₅O₃→5 Cu 2 CO₂+7 H₂O+5 N₂

The stoichiometric weight percentages are 59.2% CuO and 40.8% aminoguanidine nitrate. The adiabatic constant pressure flame temperature at 7 MPa is approximately 1815° K.

The preferred formulation uses an oxygen balance of approximately −2% which is 55% CuO and 45% aminoguanidine nitrate, by weight. This mixture's adiabatic constant pressure flame temperature at 7 MPa is approximately 1793° K.

In accordance with the present invention, the autoiginition composition may comprise a mixture of CuO as the oxidizer in a weight percentage in the range of 45% to 75%, and aminoguanidine nitrate as the fuel in a weight percentage in the range of 25% to 55%.

If higher adiabatic flame temperatures are required to cause ignition of the pyrotechnic materials contained within a gas generator or pyrotechnic device, other metal fuels such as aluminum or magnesium can be added. For example; 5% aluminum added to CuO and aminoguanidine nitrate at −2% oxygen balance has an adiabatic constant pressure flame temperature at 7 MPa of approximately 2359° K, 10% added aluminum yields approximately 2889° K and 15% added aluminum yields approximately 3371° K. In accordance with the present invention, the weight percentage of aluminum or magnesium preferably is less than 20% by weight.

The AIP compositions may be used in the form of powders, granules, or compression-molded pellets. The AIP compositions are most preferably used in the form of a solid compression-molded mixture of the above-described components. In this regard, the compositions will therefore most preferably include a polymeric binder in an amount sufficient to bind the components into a solid form (e.g., pellet). The binder will therefore typically be present in an amount. based on the total AIP composition weight, of between about 1.0 to about 5.0 wt. %, and preferably about 2.0 wt. %. The preferred binders include poly(alkylene carbonates) that are commercially available from Pac Polymers, Inc. as Q-PAC® 40, a poly(propylene carbonate) copolymer, and Q-PAC® 25, a poly(ethylene carbonate) copolymer, or mixtures thereof.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. An autoignition composition for a gas generant for inflating an airbag or the like, said autoignition composition comprising a mixture of CuO as the oxidizer in a weight percentage of 45% to 75%, and aminoguanidine nitrate as the fuel in a weight percentage of 25% to 55%.
 2. The autoignition composition of claim 1 using an oxygen balance of approximately −2% which is 55% CuO by weight and 45% aminoguanidine nitrate by weight.
 3. The autoignition composition of claim 2 wherein the adiabatic constant pressure flame temperature at 7 MPa is approximately 1793° K.
 4. The autoignition composition of claim 3 wherein the composition ignites at 150° C.
 5. The autoignition composition of claim 1 wherein a metal fuel is added to increase the flame temperature of the mixture.
 6. The autoiginition composition of claim 5 wherein the metal fuel is aluminum or magnesium.
 7. The autoignition composition of claim 6 wherein the weight percentage of magnesium or aluminum is less than 20%. 